PEP8 fix [skip ci]
PEP8 fixes [skip ci]
PEP8 fixes in circular_overlap
PEP8 fixes in elliptical_overlap
PEP8 fixes in rectangular_overlap
PEP8 fixes in utils
PEP8 fixes in tests
PEP8 fixes in aperture_funcs
Update extern.stats to match astropy merged version
Update docs with new Gaussian FWHM <-> sigma constant